Synchronization of optical protection switching and loading of path specific characteristics

ABSTRACT

Systems and methods describe synchronizing optical protection switching with an Optical Protection Switch (OPS) including a splitter on a transmit side to both a first fiber path and a second fiber path and a receive switch and monitoring port on a receive side with the receive switch set to only one of the first fiber path and the second fiber path. A method includes, responsive to detection of a fault on the first fiber path, generating a link Forward Defect Indication (FDI) and transmitting the link FDI over a messaging channel downstream; and utilizing the link FDI to generate an Optical Protection Switch Indicator (OPSI) status used by the OPS to cause a switch of the receive switch to the second fiber path.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to optical networking systemsand methods. More particularly, the present disclosure relates tosynchronization of optical protection switching and loading of pathspecific characteristics.

BACKGROUND OF THE DISCLOSURE

Protection switching in optical networks enables redundancy andresiliency to fiber cuts or other failures. At Layer 1, e.g., TimeDivision Multiplexing (TDM) such as Synchronous Optical Network (SONET),Synchronous Digital Hierarchy (SDH), etc., protection switching occursin the electrical domain (Layer 1) via synchronous signaling.Specifically, there are dedicated bytes in the frame overhead assignedfor the purpose of signaling local switch status (switch state, statusof working and protection lines, scheduled switch events, etc.) to aremote end. This provides the infrastructure for a bidirectionalswitching capability that keeps duplex traffic flows on the same path inelectrical domain. However, such synchronization framework in theoptical domain does not exist. At Layer 0, e.g., optical, to protectfiber spans against line cuts, an Optical Protection Switch (OPS) isused in some configurations to get fast traffic restoration. An OPStypically contains an optical switch in the receiving direction thatmeasures total power in both ports and switches from one port to anotherport based on loss of light (LOL) detected on that port. To protectfiber spans, OPS switch is placed in the receiving (RX) direction of thefiber spans, while the transmitting (TX) power to the fiber span isbroadcasted to protect fiber paths using a power splitter on the OPS

It is important to maintain synchronization in Layer 0 opticalprotection switching at OPSs at both ends of a link. In an opticalnetwork deployment, Layer 0 traffic is usually bi-directional. From afiber path protection perspective, it is important to ensure thattraffic in both directions experiences similar path losses and networkelements in-between. This ensures that optical channels runningbi-directionally have a similar traffic experience for opticalperformances in terms of Optical Signal-to-Noise Ratio (OSNR),non-linear penalties, Bit Error Rate (BER), latencies, and availablemargin. However, with the conventional OPS protection scheme, thatcannot be ensured as following a fiber fault, optical channels in bothdirections can experience performance deltas for an extended period oftime until the switch at the non-faulted end is manually switched.

Additionally, in such conventional protection schemes, protected fiberpaths (or spans) are designed to be maximally diverse so that with afault in one path, the other path can be operational with a fast opticalswitch. Following a fault such as a fiber cut in one path, when trucksare rolled out to re-splice the fibers, both the transmit (TX) andreceive (RX) direction fiber-pairs are put into a maintenance state sothat re-splicing can be done maintaining laser safety standards. Withthe conventional protection schemes, before such maintenance procedures,a protection switch at the non-faulted end has to be manually switchedthat triggers an unnecessary disruption in traffic. In other words, withthe conventional protection schemes, physical efforts are required toensure both fiber paths are identical in nature in terms of span loss,fiber type, physical deployment (e.g., aerial vs. ground fibers), whileeach fiber path is kept limited to a single span to minimize the path topath characteristics variations. In a real field deployment, withdiversified fiber paths used in such OPS protection schemes, maintainingthese constraints between two sets of fiber pairs is difficult toachieve.

A conventional approach for synchronization includes introducing anoptical shutter in the TX direction. When the OPS switches on the RXport, it can also trigger a shutter off and on in the TX direction, thatin turn, triggers a loss of light on the other end and hence, triggers aswitch on the other end too. However, it is a more expensive solution asthe shutter mechanism requires additional optical components, space,processing, and control. Moreover, this approach requires specialhandling on how long the shutter needs to be toggled between OFF and ONso that the switch on the other end sees the required loss of light forcertain duration to move from one RX port to another. In addition, insome cases, due to enough Amplified Spontaneous Emission (ASE) loadingon the path, the other end may not see the necessary loss of light totrigger the switch. Another drawback of using shutter/Variable OpticalAttenuators (VOAs) on the OPS is from a reliability point of view. TheOPS is a single point of failure for the services traversing it, andtherefore it is advantageous to minimize the part count (and especiallyelectrically active parts) for a low probability of failure. Due to thisuncertainty, and due to the high dependency between pre-planned ASEestimation and actual network deployment, the expensive TX shutter basedOPS hardware solution is not popular in field deployment.

BRIEF SUMMARY OF THE DISCLOSURE

In an exemplary embodiment, a method of synchronizing optical protectionswitching is described with an Optical Protection Switch (OPS) includinga splitter on a transmit side to both a first fiber path and a secondfiber path and a receive switch and monitoring port on a receive sidewith the receive switch set to only one of the first fiber path and thesecond fiber path. The method includes, responsive to detection of afault on the first fiber path, generating a link Forward DefectIndication (FDI) and transmitting the link FDI over a messaging channeldownstream; and utilizing the link FDI to generate an Optical ProtectionSwitch Indicator (OPSI) status used by the OPS to cause a switch of thereceive switch to the second fiber path. The method can further includeutilizing the OPSI status to load path specific parameters associatedwith the second fiber path. The path specific parameters can includesettings on transceivers for any of Polarization Mode Dispersion (PMD),Dynamic Group Delay (DGD), Polarization Dependent Loss (PDL), requiredline and baud rate, viable modulation formats, and transmit power to beused for the second fiber path. The method can further includemonitoring power by the monitoring port and utilizing the OPSI status toindicate a change in gain of a pre-amplifier based on a measured powerdifference. In a transmit direction, the path specific parameters caninclude one or more of amplifier gain and actuator settings for eachpath, wherein the path specific parameters are saved duringinstallation, and wherein the path specific parameters are loaded basedon the OPSI status.

The method can further include preventing a switch of the receive switchat a local node responsive to the detection of the fault and performingthe switch of the receive switch based on the OPSI status. The methodcan further include receiving the OPSI status at a far end node andtriggering a switch of the receive switch therein to a port noted in theOPSI status such that both a local node and the far end node aresynchronized and on the second fiber path. The monitoring port can beutilized for the detection and the OPSI status is used for the switch ofthe receive switch. The messaging channel can include one of an OpticalSupervisory Channel (OSC) and General Communication Channel (GCC) bytesin overhead. The detection can be from a receiving node on the firstfiber path and the receiving node generates the link FDI and the OPSIstatus. The detection can be from an intermediate node on the firstfiber path and the intermediate node generates the link FDI and areceiving node generates the OPSI status.

In another exemplary embodiment, an optical network with at least twonodes configured to synchronize optical protection switching with anOptical Protection Switch (OPS) includes a first node including a firstOPS and a second node including a second OPS, each of the first OPS andthe second OPS include a splitter on a transmit side to both a firstfiber path and a second fiber path and a receive switch and monitoringport on a receive side with the receive switch set to only one of thefirst fiber path and the second fiber path, wherein the first node isconfigured to, responsive to detection of a fault on the first fiberpath, generate a link Forward Defect Indication (FDI) and transmit thelink FDI over a messaging channel downstream, and utilize the link FDIto generate an Optical Protection Switch Indicator (OPSI) status used bythe first OPS to cause a switch of the receive switch to the secondfiber path. The first node can be further configured to utilize the OPSIstatus to load path specific parameters associated with the second fiberpath. The path specific parameters can include settings on transceiversfor any of Polarization Mode Dispersion (PMD), Dynamic Group Delay(DGD), Polarization Dependent Loss (PDL), required line and baud rate,viable modulation formats, and transmit power to be used for the secondfiber path.

The first node can be further configured to monitor power by themonitoring port and utilizing the OPSI status to indicate a change ingain of a pre-amplifier based on a measured power difference. The firstnode can be further configured to prevent a switch of the receive switchat a local node responsive to the detection of the fault and performingthe switch of the receive switch based on the OPSI status. The secondnode can be configured to receive the OPSI status and trigger a switchof the receive switch therein to a port noted in the OPSI status suchthat both the first node and the second node are synchronized and on thesecond fiber path. The monitoring port can be utilized for the detectionand the OPSI status is used for the switch of the receive switch. Themessaging channel can include one of an Optical Supervisory Channel(OSC) and General Communication Channel (GCC) bytes in overhead.

In a further exemplary embodiment, an optical node configured tosynchronize optical protection switching of an Optical Protection Switch(OPS) with another node includes the OPS including a splitter on atransmit side to both a first fiber path and a second fiber path and areceive switch and monitoring port on a receive side with the receiveswitch set to only one of the first fiber path and the second fiberpath; a shelf processor communicatively coupled to the OPS; and amessaging channel system, wherein the optical node is configured to,responsive to detection of a fault on the first fiber path, generate alink Forward Defect Indication (FDI) and transmit the link FDI over themessaging channel system downstream, and utilize the link FDI togenerate an Optical Protection Switch Indicator (OPSI) status used bythe OPS to cause a switch of the receive switch to the second fiberpath.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated and described herein withreference to the various drawings, in which like reference numbers areused to denote like system components/method steps, as appropriate, andin which:

FIG. 1 is a network diagram of an optical network with OPS protectedfiber spans between two nodes;

FIG. 2 is a flowchart of a messaging framework process for use in theoptical network of FIG. 1 with the OPSs;

FIG. 3 is a network diagram of the network of FIG. 1 implementing themessaging framework process of FIG. 2;

FIG. 4 is a network diagram of a network with different length fiberpaths implementing the messaging framework process of FIG. 2; and

FIG. 5 is a flowchart of a process of synchronizing optical protectionswitching.

DETAILED DESCRIPTION OF THE DISCLOSURE

Again, in various exemplary embodiments, the present disclosure relatesto synchronization of optical protection switching and loading of pathspecific characteristics. Systems and methods described herein providefield-based Layer 0 restoration against optical fiber faults between twooptical nodes protected with Optical Protection Switches (OPSs) andredundant optical fiber paths. More precisely, the systems and methodsestablished a unique messaging framework between two OPS protected nodesagainst fiber path faults so that the fiber protection switching betweenthe two nodes will always remain synchronized to the same fiber path. Inaddition, the systems and methods allow each OPS protected node to takethe advantage of an OPS switching indication to set up path specificphotonic parameters such as gain and loss settings on photonic actuatorsas well as pre-loading path specific characteristics such as dispersion,group delay, etc. on Dense Wavelength Division Multiplexing (DWDM)transponders so that following the switch from one fiber path to theother, similar optical performance can be achieved for traffic in bothdirections and receiver (RX) re-acquisition time can be minimized. Thesystems and methods not only synchronize protected fiber paths, but alsoensures proper path specific settings (such as gain or loss targets) forphotonic actuators so that on a switch from one path to another, noperformance impact (due to overshoot or undershoot in power) is observedin downstream of the protected paths that can potentially be differentin nature.

The messaging framework can operate over an Optical Supervisory (orService) Channel (OSC), overhead communications channel, out-of-bandcommunications channel, etc. The messaging framework ensures both endsof a link or spans have their OPSs synchronized. This messagingframework is for the optical switches, not for electrical switches.Also, the optical switches are not integrated with corresponding opticaltransceivers (TX/RX). Stated differently, any switch by the opticalswitches (OPSs) are not triggered by the TX/RX but rather by measuringpower (i.e., the OPSs are distinct and separate from the opticaltransceivers). Further, the signaling between the optical switches overthe messaging framework uses a communication channel that is out-of-bandwith respect to the traffic being protected. Advantageously, themessaging framework enables loading path specific actuators settingsboth photonic actuators and associated optical transceivers following anoptical switch in the OPS to ensure guaranteed optical performance andminimized RX re-acquisition time.

Conventional OPS System

Referring to FIG. 1, a block diagram illustrates an optical network 10with OPS protected fiber spans between two nodes 12, 14. The two nodes12, 14 are interconnected by two fiber pairs, denoted as path 1 16, path2 18. The paths 16, 18 can be diverse, even of differing lengths withintermediate equipment such as optical amplifiers (omitted in FIG. 1).The nodes 12, 14, each include an OPS 20, an Optical Supervisory Channel(OSC) 22, an amplifier 24, and a shelf processor 26. For illustrationpurposes, the optical transceivers which connect to the amplifiers 24(either directly or through DWDM multiplexing equipment) are omitted.The amplifiers 24 can be Erbium Doped Fiber Amplifiers (EDFAs) or thelike, acting as a post-amplifier on a transmit side and a pre-amplifieron a receive side. The OSC 22 can be an out-of-band (from the amplifierand/or from the DWDM channels) wavelength which provides Operations,Administration, Maintenance, and Provisioning (OAM&P) communication. Forexample, the OSC 22 can be at 1510 nm, 1625 nm, or the like. The OSCwavelength is added/dropped with filters in the OSC 22. Also, the OSC 22can include transceiver components to enable the OSC wavelength andelectrical components for modulating/demodulating the OSC wavelength.

Thus, after the optical transceivers (not shown), the amplifier 24, andthe OSC 22, there is a single pair of signals 28—TX and RX—whichinterface the OPS 20. Functionally, the OPS 20 takes the single pair ofsignals 28 and presents two pairs of signals 30, one for each of thepaths 16, 18. Thus, the function of optical protection is to interface asingle transceiver with optical line protection over the paths 16, 18.To support this optical protection, on the transmit side, the OPS 20includes a splitter 32 which splits the transmit signal from the signals28 to fibers in each of the paths 16, 18. Thus, the OPS 20 includestransmitting actively over both of the paths 16, 18. On the receiveside, the OPS 20 includes a switch 34 which selects only one fiber fromeach of the paths 16, 18 based on a monitoring port 36. Specifically, aLoss of Light (LOL) on the monitoring port 36 causes the switch 34 totoggle.

In operation, when a fiber cut (i.e., an optical line fail (OLF)) takesplace on the active fiber path (step 40-1), the active OPS RX port atthe node 14, where the switch is currently set (e.g. port #4 for thesignals 30) goes into a loss of light (LOL) state, the OPS 20 does anautomatic switch to the other RX port (e.g. port #6 for the signals 30)(step 40-2). However, in the reverse direction, since the node 12's OPS20 active RX port #4 does not experience a LOL condition, the switchremains set at its current location (port #4) (step 40-3). That bringsthe switch ports at both ends switched at different fiber paths 16, 18that could potentially be different in length, fiber-type, span loss, oreven from network topology perspective (i.e., one path may contain morenetwork elements than the other path).

Messaging Framework Process

Referring to FIG. 2, in an exemplary embodiment, a flowchart illustratesa messaging framework process 50 for use in the optical network 10 withthe OPSs 20. The systems and methods establish a messaging frameworkbetween OPS protected nodes 12, 14 against fiber paths so that the fiberprotection switching between the two nodes 12, 14 will always remainin-sync to the same fiber path 16, 18. The messaging framework process50 allows each OPS protected node to take advantage of an OPS switchingindication to setup the path specific photonic parameters. The pathspecific photonic parameters can include target gain settings on thepre- and post-amplifiers, per channel actuator settings if the OPS 20 isassociated with an OADM node both for the mux and demux directions, andpath specific restoration and acquisition settings on the opticaltransceiver, if the optical transceiver is associated with the OPSprotected nodes 12, 14. Such settings on the optical transceiver includepre-saving path specific characteristics for receivers (RX) such asPolarization Mode Dispersion (PMD), Dynamic Group Delay (DGD),Polarization Dependent Loss (PDL), or path specific requirements fortransmitters (TX) such as required line and baud rate, viable modulationformats, transmit power to be used for one fiber path versus the other,and loading up the path specific settings on the optical transceiver insync with the OPS 20 switching from one path to the other. This helps toreduce RX re-acquisition time significantly as well as allows theoptical transceiver to be setup in a configuration protected by the OPS20 against line fiber faults with diversified optical paths 16, 18 bothin terms of length, fiber type, and topology.

In FIG. 1, the messaging framework process 50 works on the nodes 12, 14with the OPS 20 protecting against two or more fiber paths 16, 18 witheach path 16, 18 including a TX and RX fiber. The messaging frameworkprocess 50 and the OPS 20 deal with fiber faults such as line fiber cutsor the like. The messaging framework process 50 operates between the OPS20, the OSC 22, the amplifier 24, the shelf processor 26, and theassociated optical transceivers. Specifically, the OPS 20 providesdetection and switching functionality for the optical protection, andthe OPS 20 is communicatively coupled to the shelf processor 26. Theshelf processor 26 is a nodal controller associated with the nodes 12,14 and configured to perform OAM&P functionality associated with thenodes 12, 14. The shelf processor 26 is also communicatively coupled tothe OSC 22 for communication with adjacent nodes and their shelfprocessors 26. The shelf processor 26 is further communicatively coupledto the amplifiers 24 and optical transceivers for distribution of thepath specific photonic parameters.

The messaging framework process 50 initiates with detection of a fiberfault by a detecting node (step 51). The fiber fault is detected by theOPS 20, such as by the monitoring port 36 detecting a loss of light, biterrors, or some other condition. The messaging framework process 50includes an automatic protection switch by the OPS 20 is blocked whenthe active receiving port goes into a Loss of Light (LOL) state (step52). Thus, with the messaging framework process 50, the OPS 20protection switch is not automatic, but only aftersynchronization/signaling with the far end. After blocking theprotection switch, the messaging framework process 50 includes each nodewith Loss of Signal (LOS) detected over the OSC 22 or with thepre-amplifier in a shutoff state generating a link Forward DefectIndicator (FDI) flag (step 53). The link FDI flag is propagated towardsdownstream of the fault from node to node until the flag arrives at anoptical section boundary or a node protected with the OPS 20 againstfiber paths, whichever comes first (step 54). At this boundary or nodereceiving the link FDI flag, if this is not protected with the OPS 20,the link FDI flag continues to propagate downstream (step 56).

Once the node (“receiving node”) receives the link FDI flag at theremote end, the link FDI flag is converted to an Optical ProtectionSwitch Indicator (OPSI) status (step 57). The OPSI status is tocommunicate the fault to the OPS 20, basically converting the link FDIfrom the OSC 22 to commands for the OPS 20. The receiving node checks ifthe other OPS 20 RX port is in an LOS state (step 58), and if so, thereceiving node keeps monitoring the power level on the other RX port(step 59). Specifically, the receiving node can periodically check thatthe other RX port is available, but there is no reason to switch if theother RX port is in the LOS state. If the other RX port is not in theLOS state (step 58), the receiving node switches the OPS 20 to the otherfiber path and uses that to trigger pre-loading path specific gain andloss settings on the corresponding actuators and transponder parameters(step 60).

The receiving node sends the OPSI status and the current switch portnumber in the reverse direction (step 61). This ensures synchronizationbetween the detecting node and the receiving node. The OPSI status ispropagated from node to node using the messaging infrastructure (e.g.,the OSC 22) and intercepted by a node only if that node is OPS protectedagainst fiber paths, i.e., the detecting node (step 62). The far endnode, the detecting node, receives the OPSI status and associated switchport number, and switches the OPS 20 to that fiber path regardless ofpower status at RX port, and uses the switch indication to triggerpre-loading path specific gain and loss settings on correspondingactuators and transponder parameters (step 63). Finally, the messagingframework process 50 ends (step 64).

Conventionally, the OPS 20 automatically switches as soon as thereceiving port, where the switch is currently set, goes into LOS or LOLstate i.e. the measured power level goes below a certain threshold. Themessaging framework process 50 stops the automatic OPS switch based onlocal detection of the LOL, LOS, etc. and instead relies on messagingbetween the nodes 12, 14 that are OPS 20 protected with each otheragainst redundant fiber paths following fiber faults on the active path.This messaging synchronizes the OPS 20 switching to trigger the switchfrom the faulted path to the other path.

Exemplary Operations of the Messaging Framework Process

Referring to FIG. 3, in an exemplary embodiment, a network diagramillustrates the network 10 implementing the messaging framework process50. FIG. 3 illustrates the same network 10 as in FIG. 1 where the fiberpaths 16, 18 are between the nodes 12, 14. Assume that both at the nodes12, 14, the OPS 20 switch is set to the fiber path 16 at the receivingdirection (port #4), the sequence of events with respect to time thattakes place between the two OPS protected nodes is illustrated asfollows. First, a fiber cut takes place on the TX fiber from the node 12to the node 14 on the fiber path 16 (step 80-1). The OPS 20 active RXport goes into the LOS state (step 80-2). The messaging frameworkprocess 50 prevents the automatic switching of the OPS 20 to the otherswitch port. The pre-amplifier goes into shutoff state at the node 14.

At the node 14, with the OSC 22 in the LOS condition and thepre-amplifier in the shutoff state (due to low power, the amplifiershuts off), the node 14 raises the link FDI flag to notify the forwarddirection nodes of the fault (step 80-3). The link FDI flag ispropagated until it reaches an optical section boundary, or a node withOPS protection, whichever comes first (in this case, the node 12). Ifthe OPS 20 is present to protect against fiber faults, the node 16converts the link FDI flag to the OPSI status and switches the OPS 20 tothe other RX to the fiber path 18 (step 80-4). That is, instead ofallowing the OPS 20 to blindly switch to the other RX port just based onthe LOS detection on the active port, the messaging framework process 50switches the OPS 20 to the other RX port, only when either an OPSI flagis locally raised, or received from an upstream node and the other RXport is not in LOS state. The link FDI flag is terminated at the node14.

Assuming there is no fiber fault on the fiber path 18, power should bepresent at the other OPS RX port at the node 14, and switching the OPS20 should clear the shutoff condition at pre-amplifier (step 80-5). Thenode 14 sends the OPSI status and associated switch port number, e.g.,OPSI <6> in the reverse direction (step 80-6). The OPSI flag ispropagated from node to node using the messaging infrastructure untilthe flag reaches the node 12 protected with the OPS 20. At the far end,the node 12 receives the OPSI <#> status, and triggers a switch to thesame port, e.g. <6>, on the OPS 20 (step 80-7). At this state, both thenodes 12, 14 are successfully switched to fiber pair path 2, and traffichas now been fully recovered.

In addition to switching the OPS from one fiber path 16, 18 to theother, the messaging framework process 50 also uses the switchindication to trigger pre-loading path specific gain and loss settingson corresponding actuators and associated transponder parameters, ifany. For example, at the network setup illustrated in FIG. 3, typicallyat each node 12, 14, the pre-amplifier gain is adjusted to compensatefor the incoming span loss. At the nodes 12, 14, when the OPS 20switches from one RX port to another, the proposed messaging frameworkprocess 50 knows the OPS 20 protection in place, monitors the totalpower received at each RX port of the OPS 20, takes the received powerdelta in account between two RX ports (in this example, port 4 and port3), and uses the OPS switch indication to trigger a change in the gainof the pre-amplifier by that measured power delta amount. Similarly, onthe transmit (RX) direction if the fiber type is different and requiresdifferent launch power target to minimize non-linear propagationpenalties or to improve OSNR compared to one fiber path to the other,then the messaging framework process 50 allows to pre-program such deltaduring node installation time frame, and such delta can be used tore-adjust the post-amplifier gain targets or per channel actuatorattenuation settings following the switch in the OPS 20.

In this way, the messaging framework process 50 avoids any overshoot orundershoot in downstream spans due to incoming path loss variationsbetween protected fiber paths 16, 18 as well as minimized performancepenalties due to fiber type and loss variations.

In addition, at the initial state of topology discovery, when each node12, 14 discovers the presence of neighboring nodes using the existingmessaging infrastructure, each OPS protected node sends out the OPSIstatus flag in reverse direction, and if the local switch port locationdoes not match with the far end switch port location (received throughOPSI status flag), then each OPS protected node raises a user-visibleOPS switch mismatch warning or alarm. This way, the messaging frameworkprocess 50 ensures the OPS 20 switches at both ends is in-sync atinitial network deployment condition. While the OPS switch ports arein-sync, the messaging framework process 50 allows each locallyassociated TX/RX (transmit/receive) to save path specificcharacteristics for receivers (RX) such as Polarization Mode Dispersion(PMD), Dynamic Group Delay (DGD), Polarization Dependent Loss (PDL), orpath specific requirements for transmitters (TX) such as line and baudrate, viable modulation formats, transmit power so that these settingscan be pre-loaded at TX/RX if necessary both to reduce RX re-acquisitiontime and avoiding manual path specific usage settings on the TX.

Other than fiber cuts, for other traffic affecting line faults, such asthe Automatic Power Reduction (APR) events on the amplifiers 24 due tohigh back reflection and laser safety, or due to high fiber loss eventson the span, or even for photonic circuit pack fail events, themessaging framework process 50 can be used to trigger optical switch atboth ends from one fiber path 16, 18 to another. Also, compared toconventional approaches, where a manual OPS switch is required duringfiber fault repair states, the messaging framework process 50 avoidsunnecessary traffic disruption by avoiding that manual switch beforefiber fault recovery.

In terms of generating the OPSI flag, in the illustration examples, themethod used OPS switch port number to associate with the flag. Analternate option is to assign a logical path identifier for each fiberpath that is unique to the set of redundant fiber paths and maintainedthe same path id at both OPS protected nodes. In such case, at theswitch at one end, the node associates the logical fiber path id withthe OPSI flag to propagate that to the reverse end. The advantage ofusing this scheme of its usability in 1+N fiber protection setups, whereN is the number of redundant fiber paths.

For illustration purposes, the messaging framework process 50 relies onmessaging infrastructure from node to node using signaling betweenswitches with a communication channel that is out-of-band with respectto the traffic being protected such as the OSC 22. However, themessaging framework process 50 can work with other communicationtechniques as well, such as the General Communication Channel (GCC) inOptical Transport Network (OTN).

Referring to FIG. 4, in an exemplary embodiment, a network diagramillustrates a network 100 with different length fiber paths 16, 18implementing the messaging framework process 50. Here, the fiber path 16includes intermediate amplifier nodes 102, 104 which can participate inthe messaging infrastructure, but which do not include OPSs 20. Theresponsibility of the intermediate amplifier nodes 102, 104 is to relaythe link FDI flag to downstream nodes. Using the messaging frameworkprocess 50, it is possible to achieve fiber path protection between twonodes even if the OPS 20 switch is configured at the transmittingdirection, or both at transmit and receive direction. The workflow ofthe messaging framework process 50 in such protection configuration isillustrated in the network 100, where the nodes 12, 14 are protectedwith two different fiber paths 16, 18. Each fiber path 16, 18 issignificantly diversified in characteristics from the other path. Forillustration purposes, the path 16 contains additional nodes such as theintermediate amplifier nodes 102, 104 between the nodes 12, 14, whilethe path 18 is a direct fiber span connection between the nodes 12, 14.To illustrate, assume that at the nodes 12, 14, the OPS 20 switch is setto the fiber path 16 at the transmitting (TX) direction (port #6).

For illustration purposes, a fiber cut takes place in the direction fromthe node 12 to the node 102 in the fiber path 16 (step 120-1). At thenode 102, with the OSC 22 in an LOS condition and the pre-amplifier inshutoff, the node 102 raises a link FDI flag to notify fiber faultcondition to forward direction nodes. The link FDI flag is propagatedfrom node to node until it hits an optical section boundary, or a nodewith OPS protection for fiber paths, whichever comes first, here thenode 14. The node 14 receives the link FDI flag. Since the OPS 20 ispresent to protect against fiber faults, the node 14 converts the linkFDI flag to an OPSI status, and switch the OPS 20 at the transmittingdirection to the fiber path 18 (step 120-2). The pre-amplifier stays inshutoff state at this point at the node 14. The node 14 sends the OPSIstatus and associated switch port number, e.g., OPSI <4>, in the reversedirection (step 120-3). The OPSI status flag is propagated in reversedirection from node to node using the messaging infrastructure until theflag reaches a node protected with OPS (e.g., the node 12) (step 120-4).At the far end, the node 12 receives the OPSI <#> status and triggersthe TX switch to the same port, e.g., <4> (step 120-5). At this stage,at the node 14, the OSC LOS and LOF conditions clear, and thepre-amplifies comes out of shutoff state, and traffic gets restored inboth directions (step 120-6).

In such configuration (where the OPS switch is configured for the TXdirection), amplifier gain and actuator loss settings for each path arepre-saved during topology discovery state or during installation timeand later updated when a path becomes active, and those path specificgain, loss for photonic actuators, and non-linear value settings forTX/RX are used when the OPS switch takes place following the receipt oflink-FDI or OPSI status flag.

There are few advantages and disadvantages of placing the opticalprotection switch in the transmit direction. For example, the task ofshutting off power into the failed path (for eye safety) is addressed insuch configuration by switching away light from the faulted fiber path,although the head-end switch has to be blind due to inability to detectviability of the protection path since there is no signal feeding intoit, in addition to timing overhead compared to a tail-end switch.However, the key point is, the messaging framework process 50 to sync-upoptical switches and loading path specific characteristics at twodistinct nodes to protect against fiber path faults works regardless ifthe optical switch is placed at the transmit (head-end) or at thereceive (tail-end) or at both, and for both 1+1 and 1+N fiber pathprotection schemes, where N is the number of redundant protection fiberpaths.

Process of Synchronizing Optical Protection Switching

Referring to FIG. 5, in an exemplary embodiment, a flowchart illustratesa process 200 of synchronizing optical protection switching. The process200 uses an Optical Protection Switch (OPS) including a splitter on atransmit side to both a first fiber path and a second fiber path and areceive switch and monitoring port on a receive side with the receiveswitch set to only one of the first fiber path and the second fiberpath. The process 200 includes, responsive to detection of a fault onthe first fiber path, generating a link Forward Defect Indication (FDI)and transmitting the link FDI over a messaging channel downstream (step201); and utilizing the link FDI to generate an Optical ProtectionSwitch Indicator (OPSI) status used by the OPS to cause a switch of thereceive switch to the second fiber path (step 202).

The process 200 can include utilizing the OPSI status to load pathspecific parameters associated with the second fiber path (step 203).The path specific parameters can include settings on transceivers forany of Polarization Mode Dispersion (PMD), Dynamic Group Delay (DGD),Polarization Dependent Loss (PDL), required line and baud rate, viablemodulation formats, and transmit power to be used for the second fiberpath. The process 200 can include monitoring power by the monitoringport and utilizing the OPSI status to indicate a change in gain of apre-amplifier based on a measured power difference (step 204). In atransmit direction, the path specific parameters can include one or moreof amplifier gain and actuator settings for each path, wherein the pathspecific parameters are saved during installation, and wherein the pathspecific parameters are loaded based on the OPSI status.

The process 200 can include preventing a switch of the receive switch ata local node responsive to the detection of the fault and performing theswitch of the receive switch based on the OPSI status (step 205). Theprocess 200 can include receiving the OPSI status at a far end node andtriggering a switch of the receive switch therein to a port noted in theOPSI status such that both a local node and the far end node aresynchronized and on the second fiber path (step 206). The monitoringport can be utilized for the detection and the OPSI status can be usedfor the switch of the receive switch. The messaging channel can includeone of an Optical Supervisory Channel (OSC) and General CommunicationChannel (GCC) bytes in overhead. The detection can be from a receivingnode on the first fiber path and the receiving node generates the linkFDI and the OPSI status. The detection can be from an intermediate nodeon the first fiber path and the intermediate node generates the link FDIand a receiving node generates the OPSI status.

In another exemplary embodiment, an optical network with at least twonodes configured to synchronize optical protection switching with anOptical Protection Switch (OPS) includes a first node including a firstOPS and a second node including a second OPS, each of the first OPS andthe second OPS include a splitter on a transmit side to both a firstfiber path and a second fiber path and a receive switch and monitoringport on a receive side with the receive switch set to only one of thefirst fiber path and the second fiber path, wherein the first node isconfigured to, responsive to detection of a fault on the first fiberpath, generate a link Forward Defect Indication (FDI) and transmit thelink FDI over a messaging channel downstream, and utilize the link FDIto generate an Optical Protection Switch Indicator (OPSI) status used bythe first OPS to cause a switch of the receive switch to the secondfiber path.

In a further exemplary embodiment, an optical node configured tosynchronize optical protection switching of an Optical Protection Switch(OPS) with another node includes the OPS including a splitter on atransmit side to both a first fiber path and a second fiber path and areceive switch and monitoring port on a receive side with the receiveswitch set to only one of the first fiber path and the second fiberpath; a shelf processor communicatively coupled to the OPS; and amessaging channel system, wherein the optical node is configured to,responsive to detection of a fault on the first fiber path, generate alink Forward Defect Indication (FDI) and transmit the link FDI over themessaging channel system downstream, and utilize the link FDI togenerate an Optical Protection Switch Indicator (OPSI) status used bythe OPS to cause a switch of the receive switch to the second fiberpath.

It will be appreciated that some exemplary embodiments described hereinmay include one or more generic or specialized processors (“one or moreprocessors”) such as microprocessors; Central Processing Units (CPUs);Digital Signal Processors (DSPs): customized processors such as NetworkProcessors (NPs) or Network Processing Units (NPUs), Graphics ProcessingUnits (GPUs), or the like; Field Programmable Gate Arrays (FPGAs); andthe like along with unique stored program instructions (including bothsoftware and firmware) for control thereof to implement, in conjunctionwith certain non-processor circuits, some, most, or all of the functionsof the methods and/or systems described herein. Alternatively, some orall functions may be implemented by a state machine that has no storedprogram instructions, or in one or more Application Specific IntegratedCircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic or circuitry. Ofcourse, a combination of the aforementioned approaches may be used. Forsome of the exemplary embodiments described herein, a correspondingdevice in hardware and optionally with software, firmware, and acombination thereof can be referred to as “circuitry configured oradapted to,” “logic configured or adapted to,” etc. perform a set ofoperations, steps, methods, processes, algorithms, functions,techniques, etc. on digital and/or analog signals as described hereinfor the various exemplary embodiments.

Moreover, some exemplary embodiments may include a non-transitorycomputer-readable storage medium having computer readable code storedthereon for programming a computer, server, appliance, device,processor, circuit, etc. each of which may include a processor toperform functions as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, an optical storage device, a magnetic storage device, a ROM(Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM(Erasable Programmable Read Only Memory), an EEPROM (ElectricallyErasable Programmable Read Only Memory), Flash memory, and the like.When stored in the non-transitory computer readable medium, software caninclude instructions executable by a processor or device (e.g., any typeof programmable circuitry or logic) that, in response to such execution,cause a processor or the device to perform a set of operations, steps,methods, processes, algorithms, functions, techniques, etc. as describedherein for the various exemplary embodiments.

Although the present disclosure has been illustrated and describedherein with reference to preferred embodiments and specific examplesthereof, it will be readily apparent to those of ordinary skill in theart that other embodiments and examples may perform similar functionsand/or achieve like results. All such equivalent embodiments andexamples are within the spirit and scope of the present disclosure, arecontemplated thereby, and are intended to be covered by the followingclaims.

1. A method of synchronizing optical protection switching with anOptical Protection Switch (OPS) including a splitter on a transmit sideto both a first fiber path and a second fiber path, and a receive switchand monitoring port on a receive side with the receive switch set toonly one of the first fiber path and the second fiber path, the methodcomprising: responsive to detection of a fault on the first fiber path,generating a link Forward Defect Indication (FDI) and transmitting thelink FDI over a messaging channel downstream; and utilizing the link FDIto generate an Optical Protection Switch Indicator (OPSI) status used bythe OPS to cause a switch of the receive switch to the second fiberpath.
 2. The method of claim 1, further comprising: utilizing the OPSIstatus to load path specific parameters associated with the second fiberpath.
 3. The method of claim 2, wherein the path specific parameterscomprise settings on transceivers for any of Polarization ModeDispersion (PMD), Dynamic Group Delay (DGD), Polarization Dependent Loss(PDL), line and baud rate, viable modulation formats, and transmit powerto be used for the second fiber path.
 4. The method of claim 2, furthercomprising: monitoring power by the monitoring port and utilizing theOPSI status to indicate a change in gain of a pre-amplifier based on ameasured power difference.
 5. The method of claim 2, wherein, in atransmit direction, the path specific parameters comprise one or more ofamplifier gain and actuator settings for each path, wherein the pathspecific parameters are saved during installation, and wherein the pathspecific parameters are loaded based on the OPSI status.
 6. The methodof claim 1, further comprising: preventing a switch of the receiveswitch at a local node responsive to the detection of the fault andperforming the switch of the receive switch based on the OPSI status. 7.The method of claim 1, further comprising: receiving the OPSI status ata far end node and triggering a switch of the receive switch therein toa port noted in the OPSI status such that both a local node and the farend node are synchronized and on the second fiber path.
 8. The method ofclaim 1, wherein the monitoring port is utilized for the detection andthe OPSI status is used for the switch of the receive switch.
 9. Themethod of claim 1, wherein the messaging channel comprises one of anOptical Supervisory Channel (OSC) and General Communication Channel(GCC) bytes in overhead.
 10. The method of claim 1, wherein thedetection is from a receiving node on the first fiber path and thereceiving node generates the link FDI and the OPSI status.
 11. Themethod of claim 1, wherein the detection is from an intermediate node onthe first fiber path, and the intermediate node generates the link FDIand a receiving node generates the OPSI status.
 12. An optical networkwith at least two nodes configured to synchronize optical protectionswitching with an Optical Protection Switch (OPS), the optical networkcomprising: a first node including a first OPS and a second nodeincluding a second OPS, each of the first OPS and the second OPSincludes a splitter on a transmit side to both a first fiber path and asecond fiber path, and a receive switch and monitoring port on a receiveside with the receive switch set to only one of the first fiber path andthe second fiber path, wherein the first node is configured to,responsive to detection of a fault on the first fiber path, generate alink Forward Defect Indication (FDI) and transmit the link FDI over amessaging channel downstream, and utilize the link FDI to generate anOptical Protection Switch Indicator (OPSI) status used by the first OPSto cause a switch of the receive switch to the second fiber path. 13.The optical network of claim 12, wherein the first node is furtherconfigured to utilize the OPSI status to load path specific parametersassociated with the second fiber path.
 14. The optical network of claim13, wherein the path specific parameters comprise settings ontransceivers for any of Polarization Mode Dispersion (PMD), DynamicGroup Delay (DGD), Polarization Dependent Loss (PDL), line and baudrate, viable modulation formats, and transmit power to be used for thesecond fiber path.
 15. The optical network of claim 13, wherein thefirst node is further configured to monitor power by the monitoring portand utilizing the OPSI status to indicate a change in gain of apre-amplifier based on a measured power difference.
 16. The opticalnetwork of claim 12, wherein the first node is further configured toprevent a switch of the receive switch at a local node responsive to thedetection of the fault and performing the switch of the receive switchbased on the OPSI status.
 17. The optical network of claim 12, whereinthe second node is configured to receive the OPSI status and trigger aswitch of the receive switch therein to a port noted in the OPSI statussuch that both the first node and the second node are synchronized andon the second fiber path.
 18. The optical network of claim 12, whereinthe monitoring port is utilized for the detection and the OPSI status isused for the switch of the receive switch.
 19. The optical network ofclaim 12, wherein the messaging channel comprises one of an OpticalSupervisory Channel (OSC) and General Communication Channel (GCC) bytesin overhead.
 20. An optical node configured to synchronize opticalprotection switching of an Optical Protection Switch (OPS) with anothernode, the optical node comprising: the OPS including a splitter on atransmit side to both a first fiber path and a second fiber path, and areceive switch and monitoring port on a receive side with the receiveswitch set to only one of the first fiber path and the second fiberpath; a shelf processor communicatively coupled to the OPS; and amessaging channel system, wherein the optical node is configured to,responsive to detection of a fault on the first fiber path, generate alink Forward Defect Indication (FDI) and transmit the link FDI over themessaging channel system downstream, and utilize the link FDI togenerate an Optical Protection Switch Indicator (OPSI) status used bythe OPS to cause a switch of the receive switch to the second fiberpath.